1. Field of the Invention
The present invention relates generally to a height control system in an automotive suspension system for regulating the height level of a vehicle body relative to a suspension member which rotatingly supports the vehicle wheel. More specifically, the invention relates to a height control system capable of preventing hunting in height regulating operation.
2. Description of the Background Art
Various vehicle height control or height regulation systems have been developed and applied vehicles in the market. One of the known vehicle height control system is illustrated in the Japanese Patent First (unexamined) Publication No. 58-112817, published on Jul. 5, 1983. In the shown vehicular height control system, the height level of the vehicle body relative to suspension member is monitored and height control is performed with respect to each wheel position independently of other wheel positions. Such control is generally successful in regulating vehicular attitude.
In addition, in the shown system, when a demand for increasing height of the vehicle body relative to the corresponding suspension member, which demand will be hereafter referred to as "up-demand" and a demand for decreasing height of the vehicle body, which demand will be hereafter referred to as "down-demand" simultaneously occur, height control operation for increasing height in response to the up-demand, which control operation will be hereafter referred to as "up-control", is given higher priority than height control operation for decreasing height in response to the down demand, which control operation will be hereafter referred to as "down-control".
In such a conventional suspension control system, a hunting in adjustment of the vehicular body height level occurs when balance of load distribution is broken. Namely, in a certain vehicular driving conditions gravity center of the vehicle body shifts significantly to concentrate gravitational load to two or three wheels (hereafter referred to as "loaded wheel" to cause substantially no load condition for the remaining wheel or wheels (hereafter referred to as "unloaded wheel"). By concentrating the gravitational load, relative distance between the vehicle body and loaded wheel is reduced to cause the up-demand. On the other hand, by substantial reduction of the load at the unloaded wheel, down-demand occurs at the unloaded wheel. As set forth above, since up-control is given higher priority, up-control occurs in this situation.
Generally, as is known from the art, up-control operation is performed by increasing pneumatic pressure in a pneumatic chamber provided with a suspension strut assembly. In such case, pressurized gas tends to be introduced into the pneumatic chambers of the suspension strut supporting the unloaded wheel to further increase the height of the vehicle body at the unloaded wheel. This may affect the attitute of the vehicle and affect height adjustment at the loaded wheels. As a result, over-shooting in adjustment of the height level at respective wheels tends to occur, causing hunting. This leads to an uncomfortable variation of the vehicular height level, thus degrading the riding comfort of the vehicle.